Wells may be completed through dual or side-by-side tubing strings or through concentric tubing. In both applications, access to the tubing annulus is provided. The side-by-side application allows wireline access to the annulus for the purpose of setting a seal plug in the tubing hanger. Another annulus bore seal method in the tubing hanger would eliminate the need for wireline access allowing use of a concentric design. Difficulties have been encountered in the past with the side-by-side arrangement in that orientation of the hangers has been a problem and the side-by-side arrangement is more expensive. Since concentric tubing strings greatly simplify the riser, the need for a second bore in the annulus through the riser and tree valve block is eliminated and larger production tubing sizes can be used in smaller casing.
Prior to the present invention, concentric designs have been offered which provide a sting open back pressure valve in the top of the hanger annulus through bore. This valve is stung open by the tree to ensure communication with the annulus for monitoring, killing and injecting in the tree-installed position. This design totally relies on the back pressure valve for sealing of the annulus should pressure build up in the annulus. This is not desirable since the valve cannot be tested until the tree is removed and killing the well if a pressure build-up had occurred in the annulus prior to the tree removal is usually not a preferred method of operating.
Various solutions have been offered in the past to the problem of having a valve controlling the annulus which is not reliant upon the tree stinger but can be controlled by hydraulic or wireline operations. One proposal is to use a hydraulically operated sleeve controlling one or more ports in the top of the tubing hanger but this could result in the annulus being permanently opened in the event of failure of the hydraulic control system.
Another solution has been suggested which is to use a fail safe spring with the sleeve valve. This is an improvement but still suffers from resulting in a fail open or fail closed with no other flexibility.
It has also been proposed to use a wireline operated sliding sleeve to open up or seal off annulus porting. These suggested solutions require the use of an internal sleeve valve in the production bore or an external sleeve valve which is hydraulically operated.
Down hole ball valves have long been used in production strings as shown in U.S. Pat. Nos. 3,035,808 and 3,796,257 which disclose fluid operated downhole ball valves; U.S. Pat. No. 3,601,190 which discloses a dual string pressure responsive ball valves in the parallel tubing strings; and U.S. Pat. No. 3,815,675 which discloses a single string ball valve operated by wireline.